Inulin, which has been extracted from plants for nearly 100 years with difficulty, belongs to the polysaccharide family of compounds. Inulin is composed of a mixture of polysaccharides having various molecular weights or degrees of polymerization (DP). In general, inulin consists of fructose units with β 1-2 bonds and ending in a glucose unit. The addition or subtraction of fructose units affects inulin's molecular weight or degree of polymerization (DP). Typical inulin properties are set forth in Table 1 below.
TABLE 1Typical Inulin PropertiesPropertiesAssayDescriptionAfter drying a fine white powderTasteBland, with slight sweetnessCarbohydrate content on dry solids>99.5%basis (ds)Ash (sulfated) on ds<0.2%Heavy metals (as Pb) on ds<0.5 mg/kgCaloric content on ds1.5 kcal/g
Inulin is the main carbohydrate in a variety of plants. Table 2 lists common inulin sources and the inulin concentrations therein.
TABLE 2Common Sources of InulinSourceInulin %Agave15-20Artichoke2-6Asparagus Root10-15Banana0.3Chicory Root15-20Dahlia Tuber15-20Dandelion15-20Edible Burdock (root)16Garlic15-25Jerusalem Artichoke15-20Leak10-15Onion2-6Rye0.7Salsify15-20Wheat0.4Yacon15-20
Chicory continues to be grown extensively throughout Europe, and its many varieties are harvested and processed into an assortment of products from salad greens and cattle feed to fructose and recently to inulin. Because of its ease of cultivation and harvesting, chicory has become the principal source of inulin today.
As inulin comes from the field in the chicory plant, its molecular weight depends on many factors such as time of planting, time of harvest, amount of stress, variety type, amount of time which elapsed between harvest and processing, amount of damage at harvest and other factors.
Today, inulin is approved for use as a food additive by the governments of nine European countries (Belgium, Denmark, France, Luxembourg, Netherlands, Portugal, Spain, Sweden, and Switzerland) and Japan, and its applications are varied.
Despite the approval of inulin as a food additive in many countries, the use of inulin has been limited, because of, among other things, the limited solubility and/or miscibility of inulin in water at ambient temperatures, for example, at temperatures ranging from about 25° C., and below.
One publication reports the solubility in water of inulin derived from chicory roots to be less than about 3% (% weight/volume) at 30° C., and less than about 5% (% weight/volume) at 40° C. See E. Berghofer et al., PILOT-SCALE PRODUCTION OF INULIN FROM CHICORY ROOTS AND ITS USE IN FOODSTUFFS, CROPS, Elsevier Science Publishers, B. V., A. Fuchs, Editor, 1993 (pp. 77-84).
Another publication submitted by the United Stated Department of Agriculture reports the solubility of inulin extracted from chicory roots to be less than 2 grams per 100 cc of water at 20° C. See E. Yanovsky et al., “Solubility of Inulin”, CONTRIBUTION NO. 129 FROM THE CARBOHYDRATE DIVISION, BUREAU OF CHEMISTRY AND SOILS, U.S. DEPARTMENT OF AGRICULTURE, J. Amer. Chem. Soc. 55, 3658-3633 (1933). The same publication reports lesser solubilities for inulin extracted from Dahlia.
Caloric concerns have long played a significant role in the food choice of the U.S. public, and low calorie foods have been popular for years. Foods of this category have been dominated by those products where fructose and sucrose have been replaced by an artificial sweetener which can add sweetness without the caloric impact. In particular, the success of artificial sweeteners such as saccharin, aspartame and more recently sucralose, should be noted.
Most artificial or intense sweeteners, such as saccharin and aspartame, have 180 to 300 times the sweetness of an equivalent dose of sucrose. Sucralose is a sweetener 600 times sweeter than sugar. Neotane is an intense sweetener having 8000 times the sweetness of sucrose. Food processors need to use a much lower volume of these artificial sweeteners in their low calorie foods than the volume of sugar which they replace. With dry goods (such as baked products), food processors are forced to “back fill” the volume of the removed sugar which the artificial sweeteners do not replace. This back fill product is referred to as a “bulking agent.” Bulking agents are used in a variety of products, including chewing gums, confectioneries, baking mixes, meat products, and packets containing the artificial sweetener in amounts equivalent to one or more teaspoons of sugar. The optimal bulking agents should bring the physical and chemical characteristics of sugar back to the food without adding back calories or contributing significantly to product cost.
Bulking agents are evaluated against the following criteria:                1. Significantly fewer calories than sucrose, glucose or fructose        2. Physical and chemical properties that match those of sucrose in all food applications        3. Mouthfeel comparable to sugar        4. Freedom from adhesion to lips and tongue        5. Freedom from toothpack (freedom from packing into crowns of teeth)        6. Preferrably, demonstrate existence of secondary health benefits        7. No negative side effects and completely safe at reasonable levels of consumption        8. In the dry product, freedom from caking and clumping        9. In the wet product, no settling out or fractionation upon standing        
More specifically, in order to effectively replace sucrose and fructose and their organoleptic qualities, potential bulking agents should mimic the following characteristics:
SafeStableLow calorieMinimal gastrointestinal side effectsLow costNo off-flavorsHigh solubilityLow viscosityCrystallineAbility to brownProtein/starch interactions similar to sucrose 
A major obstacle to the use of inulin as a bulking agent in foodstuffs despite its many advantages is its rather low solubility in water at ambient temperatures.
Another major obstacle to the use of inulin as a bulking agent is the presence of various amounts of glucose and fructose, which are naturally contained therein, and which have made inulin difficult to dry and difficult to handle and store. In the drying of inulin, the presence of glucose and fructose, which are hygroscopic, interferes with the drying process, unless there is a large proportion of high molecular weight inulin which dries more readily than the lower molecular weight inulin compounds. Even after drying, the hygroscopicity of glucose and fructose tends to reintroduce moisture into the product.
In the case of granular or dry inulin products, the hygroscopic activity of glucose and fructose tends to cause undesirable caking and clumping. Due to the caking and clumping, the granular or dry inulin products containing glucose and fructose are difficult to handle, store, and blend.
In addition, most inulin products used as bulking agents with artificial sweeteners heretofore have contained significant amounts of free fructose and glucose and also contained high molecular weight inulin compounds, for example, molecular weights above 2288. When such inulin products are taken by mouth, there is a formation of sticky, hard substance in the mouth caused by the insolubility of such high molecular weight inulin in the saliva at body temperatures. This sticky substance may adhere to the lips and tongue, and may pack on the crowns of the consumer's teeth. In some cases, the sticky substance forms a crusty insoluble mass in the mouth which must be chewed in order to break up.
Inulin comprises polysaccharides, fragile polymers, which are difficult to extract by classical prior methods. European Patent 787 745 illustrates one method for extraction of inulin from Jerusalem artichokes using the classical sugarbeet extraction, and then clarifying the inulin rich extraction liquid by ultrafiltration. Silver U.S. Pat. No. 5,456,893 discloses a process and apparatus for extracting inulin in a manner which does not degrade the inulin or allow the inulin to be broken down.